Herein disclosed are embodiments generally relating to electrostatographic imaging members and assemblies comprising electrostatographic imaging members and acoustic dampening means. The acoustic dampening means provide excellent acoustic dampening of the resonance modes of imaging drums. More specifically, the embodiments disclose an acoustic dampening material employed in photoreceptor and/or dielectric receptor drums to substantially eliminate acoustic noise generated by drum image receivers in electrostatographic printing machines.
The term electrostatographic is used to generally encompass the fields of electrophotography and/or ionography. Hereafter, the term “drum” and/or “electrostatographic drum” will refer to either type of imaging drum—i.e. both photoreceptor and ionographic imaging drums. Electrostatographic imaging members are well known in the art. The imaging members may be in the form of various configurations such as a flexible web type belt or cylindrical drum. The drums comprise a hollow cylindrical substrate and at least one electrostatographic coating. These drums are usually supported by a hub held in place at the end of each drum. The hub usually includes a flange extending into the interior of the drum. This flange is usually retained in place by an interference fit and/or an adhesive. An axle shaft through a hole in the center of each hub supports the hub and drum assembly. Electrostatographic imaging members may be electrophotographic members or electrographic (ionographic) members. It is well known that electrophotographic members comprise at least one photosensitive imaging layer and are imaged with the aid of activating radiation in image configuration. Similarly, electrographic imaging members comprise at least one dielectric layer upon which an electrostatic latent image is formed directly on the imaging surface by shaped electrodes, ion streams, styli and the like.
A typical electrostatographic imaging process cycle involves forming an electrostatic latent image on the imaging surface, developing the electrostatic latent image to form a toner image, transferring the toner image to a receiving member and cleaning the imaging surface. Cleaning of the imaging surface of electrostatographic imaging members is often accomplished with a doctor type resilient cleaning blade that is rubbed against the imaging surface of the imaging members.
When electrostatographic imaging members are cleaned by doctor type cleaning blades rubbing against the imaging surface to remove residual toner particles remaining on the imaging surface after toner image transfer to a receiving member, a high pitched ringing, squealing, squeaking, or howling sound can be created which is so intense that it is intolerable for machine operators. This is especially noted in drum type imaging members comprising a hollow cylindrical substrate. The sound apparently is caused by a “stick-slip” cycling phenomenon during which the cleaning blade initially “sticks” to the imaging surface and is carried in a downstream direction by the moving imaging surface to a point where resilience of the imaging blade forces the tucked blade to slip and slide back upstream where it again sticks to the photoreceptor and is carried downstream with the imaging surface until blade resilience again causes the blade to flip back to its original position. The upstream flipping motion kicks residual toner particles forward. The stick-slip phenomenon is somewhat analogous to the use of a push broom for cleaning floors where the push broom is most effective for cleaning when it is pushed a short distance and then tapped on the floor with the cycle being repeated again and again. This stick-slip phenomenon is important for effective removal of residual untransferred toner particles from an imaging surface and for prevention of undesirable toner film or toner comets from forming on the imaging surface during cleaning.
An adhesive relationship between the cleaning blade and the imaging member surface appears to contribute to the creation of the howling sound. More specifically, the stick-slip effect occurs where there is a strong adhesive interaction between the cleaning blade and the imaging surface. The howling sound appears to be caused by resonant vibration of the drum induced by the stick-slip phenomenon. Other factors contributing to creation of the screaming or howling sound may include factors such as the construction of the imaging member, the blade contacting the imaging member, the type of blade holder construction, and the like. For example, a flimsy blade holder can contribute to the howling effect. Moreover, a thinner, shorter, stubbier cleaning blade tends to contribute the howling effect. Thin imaging member drums can also lead to the howling effect. The stick-slip phenomenon also depends on the lubricating effect of toner and/or carrier materials utilized. Moreover, ambient temperatures can contribute to the creation of howling. It appears that resonance is initiated at the point of contact between the cleaning blade and the imaging member. The creation of the screaming or howling sound might be analogous to rubbing a fingertip around the edge of a wine glass. The screaming or howling noise phenomenon is especially noticeable for cylindrical photoreceptors having a hollow metal or plastic drum shaped substrate. Generally, where the imaging member is the cause of a howling sound, it will emit a ringing sound when tapped.
Some methods use to reduce the noise include adding lubricants to the toner to reduce the frictional excitation (chatter or slip stick motion), which in turn reduces the excitation energy driving the acoustic resonance, internal “silencers” of various materials and configurations inserted into the interior cavity of the photoreceptor drum to absorb the sound energy and reduce the resonance amplitude, and increasing the wall thickness of the photoreceptor drum, which in turn increases the stiffness of the drum to raise resonant frequency and reduce amplitude of vibration for any given level of excitation. For example, U.S. Pat. Nos. 7,155,143, 6,438,338, 5,669,045 and 5,960,236, which are herein incorporated by reference in their entirety, disclose internal “silencers.” However, these known methods suffer from drawbacks, such as poor fit in the drum, poor sound absorption and relatively high cost.
Thus, there is a continuing need for improved systems and apparatuses which substantially reduce acoustic resonance and thus substantially eliminate acoustic noise caused by drum photoreceptors in xerographic printing machines.